In this work I am going to outline a research approach for investigating concepts on legged locomotion with the help of bio-inspired hardware systems such as legged robots and prosthesis. I will explain why hardware models of biomechanical gait concepts are not just a nice feature but do also provide a scientific tool to demonstrate and prove the value of the conceptual insights. Hardware models share properties of conceptual models (being simplified and human-made) and of the biological system (being realistic). Thus they provide a valuable column of the bridge connecting real biological locomotion from conceptual computer simulation models and theories on legged locomotion. With assistive devices this approach can be taken one step further, namely by applying the constructed concepts to the human body and by investigating the interactions between human movement and constructed concept of this very same human motion.